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A183178
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Numbers k such that 7*(10^(2*k+1)-1)/9 - 5*10^k is prime.
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2
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0, 1, 3, 7, 10, 12, 480, 949, 1945, 7548, 8923
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OFFSET
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1,3
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COMMENTS
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Original name: Numbers n such that (7*10^(2n+1)-45*10^n-7)/9 is prime.
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REFERENCES
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C. Caldwell and H. Dubner, "Journal of Recreational Mathematics", Volume 28, No. 1, 1996-97, pp. 1-9.
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LINKS
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FORMULA
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MATHEMATICA
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Do[If[PrimeQ[(7*10^(2n + 1) - 45*10^n - 7)/9], Print[n]], {n, 3000}]
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PROG
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CROSSREFS
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KEYWORD
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nonn,base
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AUTHOR
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EXTENSIONS
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Name edited and a(1) = 0 inserted by M. F. Hasler, Feb 07 2020
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STATUS
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approved
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